Automatic analysis devices are being widely utilized that calculate, according to the Lambert-Beer law, absorbance from the amount of transmitted light obtained when a reaction solution having a sample and a reagent mixed therein is irradiated with light, and that then quantitate the concentration of a component in the sample on the basis of the amount of change in the absorbance within a certain time. In such devices, a number of reaction cells holding the reaction solution are arranged along the circumference direction of a reaction disc that is rotatably driven. Around the reaction disc, an absorbance measuring unit is disposed, and the absorbance measuring unit measures the absorbance of the reaction solution at the intervals of approximately once every 15 seconds for about 10 minutes. The measured time-series data are referred to as reaction process data, and the component in the sample is quantitated from the amount of change in a certain time.
The reaction measured by the automatic analysis device includes the two types of a color reaction using a substrate and an enzyme, and an immune agglutination reaction using an antigen and an antibody. The method of quantitating concentration by the color reaction is referred to as biochemical analysis, where the examination items may include LDH (lactic acid dehydrogenase), ALP (alkaline phosphatase), and AST (aspartate-oxoglutarate aminotransferase), for example. The method of determining substance concentration by the immune agglutination reaction is referred to as immunoassay, where the examination items may include CRP (C-reactive protein), IgG (immunoglobulin), and RF (rheumatoid factor), for example. The examination items measured by the immune agglutination reaction may include those that have a relatively low blood concentration of the component and that therefore require high-sensitivity detection. In such a case, a latex reagent in which latex particles are bonded to the antibody as a sensitizer is often used. Such immune agglutination reaction is referred to as a latex immune agglutination reaction. In the latex immune agglutination reaction, the latex particles aggregate via the component, forming an aggregate. The higher the component concentration, the greater the size of the aggregate will be after a certain time. Thus, during sample measurement, the reaction solution is irradiated with light, and the amount of change in light amount or the amount of change in absorbance in a certain time is measured. Then, the measured value is compared with a calibration measurement result of measuring a calibrator with a known concentration so as to determine the component concentration. In order to further increase the sensitivity of such latex immune agglutination reaction, a method of measuring scattered light has been attempted. For example, a system and the like have been proposed whereby transmitted light and scattered light are separated using a diaphragm, and absorbance and the scattered light are simultaneously measured.